1. Field of the Invention
The present invention relates to a compound semiconductor and a method for producing the same. More particularly, the present invention relates to a dry-etching method for a III-V group or II-VI group compound semiconductor, and to a semiconductor laser device fabricated thereby.
2. Description of the Related Art
As a conventional dry-etching technique for a compound semiconductor, a method described in Japanese Laid-Open Patent Publication No. 7-66175 is known in the art. In this method, dry-etching is performed on an In-containing compound semiconductor by using ECR-RIBE (Electron Cyclotron Resonance-Reactive Ion Beam Etching) apparatus with auxiliary coil reducing a divergence of magnetic field. In the ECR-RIBE apparatus, a primary coil and an auxiliary coil are provided so that the divergence of magnetic field in the vicinity of the sample to be etched is inhibited. In this method, chlorine, helium and nitrogen are used as the etching gas. With the flow ratio of the chlorine/nitrogen gases being equal to one or less and the internal pressure being equal to 0.5 mTorr, a cross-section which is vertical with respect to the etching mask and a smooth etching surface are obtained.
According to the above-mentioned publication, when the gas is supplied with the chlorine gas/nitrogen gas ratio being equal to one or less, the production of chlorine radicals is inhibited and the etching due to chlorine ions becomes more predominant over the etching due to chlorine radicals. This makes it. possible that ions having energy as low as several tens of eV can be used and a balance of evaporation of a chloride of In and a chloride of P can still be achieved. As a result, etching which is capable of obtaining a cross-section which is vertical with respect to the etching mask, and of obtaining a smooth etching surface can be realized.
Conventionally, the dry-etching of compound semiconductor had problems associated with roughness of the etching surface due to a large difference in vapor pressures between the reactant of a III group element and the etching gas and the reactant of a V group element and the etching gas or with difficulty in controlling cross-sectional shapes.
Dry-etching technology disclosed in the above-mentioned publication also intended to solve these problems. In this technology, nitrogen gas is added so that chlorine gas is decomposed and the amount of chlorine radicals created with chlorine ions is kept below 1/3 of the total amount of chlorine radicals and chlorine ions, thereby solving the above-mentioned problems. Also realized in the above-mentioned technology is that a pressure inside the reaction chamber is made equal to 0.5 mTorr or less in order to minimize the production of chlorine radicals. This results in desorption velocities in equilibrium of the chloride of In and the chloride of P. A feature of the above-mentioned technology is that the etching is carried out under conditions which minimize the concentration of chlorine radicals. The above-mentioned publication does not show quantitative data concerning the amount of chlorine ions produced and the etching characteristics.
Moreover, if a sample to be etched contains Al, then Al.sub.2 O.sub.3 is formed with moisture remaining in the reaction chamber, thereby preventing the etching or greatly reducing the etching rate.